Researches On The Application Of Polymer Binder In Lithium-sulfur Battery And Related Improvement

Lithium-sulfur batteries have attracted considerable attention due to its high theoretical specific capacity?1675 mAh/g?,low cost,non-toxic,and environmental friendliness,etc.In this paper,we mainly discussed the binder of the cathode material.Water soluble binder agar?AG?and oil-based binder Polyamide-6?PA6?were used instead of the traditional Polyvinylidene fluoride?PVDF?.Meanwhile,the C/S composites were prepared by hydrothermal method becuase of the large size of commercial sulfur seriously impact the release of capacity of lithium-sulfur battery.The main research includes the following three parts:?1?The hydroxyl groups of agar?AG?were partially oxidized to carboxyl groups by H₂O₂ oxidant.Oxidized agar?M-AG?is easily dissolved in water at room temperature.The FTIR results show that the M-AG has a stretching vibration peak of-C=O after oxidation.In this work,the M-AG was used as binder in lithium-sulfur battery.The good contact among the active material,the conductive agent and the current collector can be well preserved with M-AG as binders.Electrochemical performance results show that the M-AG does not participate the electrochemical reaction in lithium-sulfur battery.It delivers an initial specific discharge capacity of700 mAh/g with a high capacity retention ratio of 92.9%after 50 cycles at 0.1C.Compared with the traditional PVDF binder,M-AG binder has higher capacity release and capacity retention.?2?The structural morphology and electrochemical properties of the cathode materials were studied when PA6 as the binder of lithium-sulfur battery.Scanning electron microscope?SEM?shows that PA6 can form the loose porous structure,which ensures the wettability and conductivity of the cathode material in the electrolyte.The PA6 cathode exhibit a high initial discharge specific capacity of 871mAh/g and an excellent cyclic durability of 93.1%capacity retention ratio after 100cycles at 0.1 C.The long-term cycling performance of PA6 cathode presents an initial specific discharge capacity of 630 mAh/g with a low capacity decay rate of 0.11%per cycle at 0.5 C after 400 cycles and an initial specific discharge capacity of 540 mAh/g with a high capacity retention ratio of 94.5%at 1 C after 400 cycles.The excellent performance is because the complexation between the lithium polysulfides and the amide groups of PA6 inhibits the“shuttle”of lithium polysulfides.Meanwhile,the decrease of the regularity of the molecular chain is due to the decrease of the crystallinity of the PA6,which can buffer the volume change of the cathode material during the charging and discharging process.?3?The C/S composites?H-C/S?were prepared by hydrothermal method.We studied the structure and electrochemical properties of the material.At 0.1 C,the first reversible discharge specific capacity of H-C/S cathode material is 1000 mAh/g,which is 12.9%higher than that of G-C/S cathode material,and the capacity retention rate can reach 87.9%after 100 cycles.This is because the sulfur size in the H-C/S cathode material is smaller and the dispersion is better than that of C-S composites prepared by the mechanical grinding method?G-C/S?The low electrochemical impedance make the utilization of the active material in the H-C/S cathode material more fully than the G-C/S cathode material,resulting in a higher discharge capacity.